Background:

Up until recently, multiple sclerosis and other demyelinating syndromes were reported only rarely in rheumatoid arthritis (RA). However, since the introduction of RA therapies targeting tumour necrosis factor (TNF), numerous case reports have arisen in the literature. Currently there are very few cohort-based assessments of the incidence of demyelinating events in RA, and/or the possible influence of drug exposures. The Ontario Biologics Research Initiative (OBRI) is an innovative undertaking to promote real-world rheumatic drug surveillance. Some of the OBRI analyses make use of Ontario's administrative healthcare databases. Since universal drug coverage occurs comprehensively for Ontario residents aged >= 65 years, we were able to assess the risk for developing demyelinating events in seniors with RA, and explore for potential drug effects in this sample.

Methods:

An RA cohort was assembled from Ontario billing and hospitalization data, 19922009. Analyses were limited to subjects aged > 65 with a diagnosis of RA, who filled at least 1 prescription for an oral glucocorticoid, disease-modifying agent (DMARD) or biologic. We excluded any individuals with a diagnosis of a demyelinating event, prior to their entry into the RA cohort. Then, over 19982009, we identified all new cases of demyelinating events occurring within this cohort. Our case definition of a demyelinating event was based on one or more hospitalization diagnoses, or at least 2 billing claims diagnoses (at least 8 weeks apart, but within 2 years). Identified cases were matched (on age, sex, and date of cohort entry) to up to 5 controls from the same RA cohort. We calculated the incidence rate of demyelinating events in the cohort of seniors with RA, and described medication use in relationship to these events.

Results:

In 85,458 seniors with RA (over 614,915.5 person-years), 51 demyelinating events occurred. This provides an event rate of 8.3 events/100,000 person-years, which is comparable to recent figures for demyelinating events for seniors in the Canadian general population. Biologic exposures were rare in our cohort, and none of the cases of demyelinating events in our RA cohort had been exposed to an anti-TNF agent at the time of the event, or within the 12 months preceding the event. In both cases and controls, the most common medication exposures were NSAIDs/COXIBs, glucocorticosteroids, hydroxychloroquine, and methotrexate.

Conclusions:

We provide novel data on the incidence of demyelinating events in a cohort of seniors with RA. The incidence rate of 8.3 new demyelinating events/100,000 patient-years is comparable to recent rates for Canadian seniors. None of these events appeared to have been triggered by anti-TNF drug exposures. Estimating the risk for demyelinating events due to these agents was problematic in our sample, given relatively low drug exposure rates.